Kerrison forceps, alveolar-bone forceps, scalpels, gouges (cylindrical chisels), files, surgical bars, etc. have been used for cutting organic tissue, particularly hard tissue, in neurosurgery, orthopaedic surgery, plastic surgery, oral surgery, etc. However, cutting with scalpels, forceps such as Kerrison forceps, etc. is inefficient, requiring long hours of operation, substantial labor of an operator and highly developed skill in the case of a fine cutting operation. Surgical bars driven by air pressure have a problem in that because a drill is rotating during an operation, shaking occurs at a contact location between a bar and hard tissue and is transmitted to the hand of the operator, thus making a fine and delicate operation difficult. Also, organic tissue at a cut surface is likely to lose its activity because of frictional heat caused by the rotational cutting. Further, because of rotational movements of the drill, a surgical bar will damage vascular or neural tissue in organic tissue even by a slight touch thereto.
Surgical instruments using ultrasonic have previously been developed. There are known a surgical instrument which destroys contacting organic tissue by ultrasonic vibration of an ultrasonic vibration transmitter and then sucks to remove the destroyed tissue (disclosed, for example, in JP-B-47-39197) and a surgical instrument for incision of hard and soft organic tissue, which comprises a metallic operational part having a cutting edge (disclosed, for example, in JP-B-51-46990). However, the former surgical instrument is unsuitable for cutting to form a surface or to form or enlarge a hole because a vibrator including an operational portion having a flat surface perpendicular to the direction of vibration destroys and emulsifies a surface layer of soft organic tissue by ultrasonic vibration and sucks to remove the emulsified tissue. The latter surgical instrument incises organic tissue by a cutting edge vibrating ultrasonically. The frictional heat is generated between an operational portion and organic tissue being incised due to the vibration of the operational portion having a minimum amplitude, about 30 to 50 .mu.m, required for incision. Therefore, even when an operational portion is made of a titanium alloy having a favorable heat conductivity, the surface temperature thereof rises to several hundred degrees Celsius, so that the organic tissue at the incision surface becomes carbonized. Also, the shape of the operational portion of the latter instrument is not suitable for cutting operation.
The present invention is aimed at solving these problems of the above-mentioned conventional surgical instruments. It is an object of the present invention to provide a surgical instrument for cutting organic tissue, which has improved cutting efficiency and operational precision, can prevent the deterioration of organic tissue caused by frictional heat generated between an operational portion and the organic tissue cut by the operational portion, and can minimize the loss of the mechanical strength of the operational portion caused by heat generated during operation.